Hemicelluloses are a group of plant-derived heteropolysaccharides associated with cellulose and lignin. The most common hemicelluloses are: xylan, glucuronoxylan, arabinoxylan, glucomannan and xyloglucan. In angiosperms, the principal hemicellulose component, xylan, is a polymer of β(1-4)D-xylopyranose. In arabinoxylan, branching occurs at the C2 & C3 positions with α-L-arabinofunaose. Glucuronoxylan, also found in angiosperms, has the xylan backbone with 4-0 methylglucuronic acid branching. In addition, arabinose branching as well as acetylation may be present. Gymnosperms contain glucomannans comprised primarily of D-mannosyl and D-glucosyl residues.